Cathode ray apparatus



April 18, 1961 D. E. NORGAARD CATHODE RAY APPRATUS 5 Sheets-Sheet 1 Filed June 8, 1942 April 18, 1961 D E, NORGAARD 2,980,904

CATHODE RAY APPARATUS Inventor: Donald E. Norgaard,

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April 18, 1961 D. E. NORGAARD 2,930,904

cATHoDE RAY APPARATUS Filed June 8, 1942 5 Sheets-Shed'l 4 Pig. 8. /245 /5 o GR/o voL-rs /sl/ /SQ SS uff 35o 552 n/ss/ 113g. lla A.c.Ax1s I l l/ PLATE CURRENT cuToFF/:r nVentOrI o GR/o voLTs /5ll 550] l5" D ld. N l" ard, xls E nnnn nn /352 //n H/Fgnb. Ona 6 j ga SAIUUUUUUWLMJUULNL by )Van/7 Mm His Attorney.

' PLATE CURRENT cln'oFA-/a' Aprll 18, 1961 D. E. NORGAARD 2,980,904

CATHODE RAY APPARATUS Filed June 8, 1942 5 Sheets-Sheet 5 32 KE. 05C. n

Alva F/TER 90 PHASE .9H/FT NETWOH/f AMPLIFIER ND L /Ml TER TARGET MARKER GEN. 280

MARKER ve/VAL V 1 f i L Pig-M 275 Pig. 15.275

5/3' E 276 Pfg l0d. H/ 274 c a Inventor: Donald E Norgaarcl,

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2,980,904 Patented Apr.. 18, 1961 loATHoDF. RAY APPARATUS Donald E. Norgaard, Scotia, N.Y., assignor to General Electric Company, a corporation of New York 'Filed `.lune 8, 1942, Ser. No. 44,23.`i

1'4 lClaims. (Cl. 343-11) My invention relates to cathode ray apparatus and to circuits useful in the control thereof.'

More particularly, my invention relates to cathode ray apparatus as employed in equipment for ascertaining information with respect to distant objects, and in particular for determining distance to, and the direction of, such objects.y

In equipment asnow lemployed for these purposes,

radiant impulses are transmitted at regularly recurring intervals and after each impulse corresponding impulses resulting from the transmitted impulse, as by reason of reflection from remote objects, or due to operation of apparatus on such remote objects, are received over ya certain time interval. The ray of a cathode ray device vis deflected across its viewing .screen in a predetermined path during this interval, the deflection starting just prior to transmission of each'pulse.l During this deflection the ray is caused to be deected from such path by the transmitted pulse and by each returning pulse. These latter deflections are thus spacedr on the viewing screen along the predetermined path in sequence corresponding to the time sequence of the reception of the different impulses affecting the cathode ray. Thus, the distance on the viewing screen of any deectionproduced by a received pulse from that produced by a transmitted pulse corresponds to the distance to the remote object from which the received pulse came,'whether by reason of reflection, or by reason of the operation of yapparatus on said object.y y v f One of the objects of my invention is to provide-means Vfor use in connection with such apparatus to improve the accuracy with which the vdistance'to a remote object may he ascertained. .e

A further object of my invention is to provide improved means to select a particular received impulse, or

echo, Vand Vto utilize such selected impulse exclusively'to ascertain yinformation .with respect to the corresponding vdistant object.- A further objectief my inventionV 'is to'utilize such selected impulsev to determine with greater accuracy. the distance to Vthe remote object rand the direction thereof.. Y j

A still furtherrobject of my inventionV is to provide equipment including` further cathode V'ray oscillographs which are'controlled exclusively by the selected impulses and which are operated-in su'ch a way as to providein- .dications of the direction of the distant object infone with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings in which Figs. l and 2 taken together, 'represent an embodiment o-f my invention; Fig. 3 illustrates certain characteristics of theapparatus shown in Figs. 1 `and 2; Figs. 4 and 8 represent certain details of the equipment shown in Figs. l and 2,; Figs,y 5, lla, andy 1lb represent cerv-r it is unnecessary to consider in the present application, or the details of which are represented in other figures' ofthe drawings. The circuit connections between these various apparatus unitsrare represented by a single line on the diagram representing a single conductor and by the conventional representation of ground. lIt willbe understood that one side of each .circuit mayV -be grounded and .thereforethe grounded conductor of each circuit is notv shown on vthe drawing, only conductors carrying potential with respect to ground being shown on the drawing.

' Referring rst to Figs. l and 2 of the drawing, I have indicated at the left hand portion of Fig. l at 1, "2, 3 and 4, a plurality of directive antennae. These antennae are arranged in a single plane, in an array, and are connected through transmission lines 5, 6, 7 and 8 to a pulse transmitter 9 whereby they are supplied with periodically recurring pulses to be radiated. -These pulses raf-radiated energy may impinge upon distance Areilecting surfaces and produce echoes which are received upon the `antennae i, 2, 3 and 4. Alternatively, they may aiect apparatus mounted vupon a distant-object, suchl transmitterv from 'objectionahlyy affecting thereceiverll because Iof their high intensity. Similarly, the equipment 10" includes' means `to reduce Vattenuationfof received signals by thefoutput circuit of the transmitter. One such means isY described and illustrated in the hereinafter referred to application Serial-No. 412,452 ofv Richard C. Longfellow, fuedseptember 2e, 1941, new Patent 2,412,160, issued December 3, 1946. Such means form no 4partof my piesentfinvention and. are nowin or more planes, and to provide vimproved indications of distance. Y y t Stillfurther objects of vmy invention relatevto lcircuits vand'instrum'entalities for use in the control and opera- 'tion of'such cathode ray apparatus to produce such indications and such objects will appear as the description of my invention proceeds.` v v The novel features which I believe Kto` be characteristie-of my invention are set forth "with, particularity in the appended claims. My invention itself, however, both as `to its organizationand method-of.operation,- together common use and well known to persons skilled in the art.A It may comprise a simple diode,l not shown, con# nected acrossl the line 10 extending to the receiver at a suitable' point rand biased to be normally nonconductive and' to be rendered conductive by the intense pulses produced by the transmitter. The line 98-extending from the junction point with line 19 to the transmitter should beone having high impedance when the transmitter" is inactive so as'not to attenuate received echo'pulses.

Thettime of reception of any' pulsefafte'r 'radiation'o'f- Ythe previously transmitted pulse is dependent upon the distance tothe remote object and' is utilized vasV a AmeasureY of that distance. Accordingly, these pulses are caused to affect a cathode ray oscillograph 12 to produce an indication thereon such as that indicated at 13, from'wbich such distance may be determined.

The circle 13, which I have indicated in Fig. 2 may represent the screen of theV cathode ray oscillograph 12. .During a predetermined time including the time of emis- `sion of any transmitted pulse, the cathode ray, `or beam, lof the cathode ray oscillograph is caused to` deect horizontally across this screen ina straight' line` as indicated at 14. It is also caused to be deflected 'verticallyfrorn `this straight line byreach of the pulses affecting the recorresponding pulses were received. n 1 Y,

The time required for the cathode ray to b e ldeflected across the screen indicated at 13 may beja timecomparable to the time required for a `transmitted pulse to travel to a remote object miles away,for example,

and return to the receiving antenna. T hus, echoes from anyobjects along the effective beam of the antenna] and `within the distance of 100 miles may appear upon the Screen.

of the distance to the remoteobjects frommwhichthe It may be desirable, however, to `space theu indications t .upon the screen of such echoes more widely thereon,

and accordingly, means are provided in the equipment, includingswitches 20 and 21, whereby the beam is deected across the screen in the time required for the pulse to travel 25 miles and return. duced may then be that represented at 13. Here the transmitted pulse is represented by the somewhat wider deflection 15 and the remote object, which previously `produced the deflection 16, is indicated by deilection 16',

The indication proi whereas no deflection corresponding to deflection 17 appears upon the screen since deflection 17 is produced by an object more than 25 miles away. f `The representations within the circles 13 and 13 are somewhat exaggerated but` serve adequatelyv to indicate the principle of operation` of the apparatus.

'The control switches 2) and` 21 are connected together mechanically for unicontrol andhave two positions corresponding to these different ranges of the equipment. 1 When they are in the left hand position, the i n dication represented within the circle 13 is produced l a more accurate indication of the,V distance to an object producing an echo which may be observed upon the ilt" is highly desirable in such equipment to provide` .echoes which are shown on the Range indicator.

4 23 to produce its entire sweep during the short aperture of time in which theA echoes from that particular object are received. The received echo is then applied to the control grid of the range indicator 23 to increase the intensity thereof in response to the echo. Thus, a bright spot appears in the line produced by the cathode rayon the screen of the range indicator at a point `thereof corresponding to receiptof the echo.

Further means are also provided to produce upon the screen of the oscillograph a vertical deection of predetermined form, as, for example, the inverted V shown at 35 on the drawing, and which is movable in a manner later to be explained, to accurate coincidence with the bright spot produced by the received echo. The adjustment of this means required to produce the coincidence of the inverted V and the bright spot produced by the echo then constitutes the required more accurate criterion of distance to the object producing the echo. The means for effecting this adjustment, and the operation thereof,

will be fully explained in connection with Figs. 2 and 9.

i In the left hand portion of Fig. 2 two additional cathode ray'oscillographs 50 and 51 are shown, the rst of which `bears the legend Elevation and the second of which bears the legend Train These cathode ray oscillographs respond likewise only to echoes which occur during thesame aperture of time during which the range indicator responds. They thus vrespond only toThe @Y areutilized to indicate the direction of the object producing this echo whichis "received during this aperture of time. These cathode yrayoscillographs are controlled by mechanism 52 by whichthe directional properties of the antennae` array 1, 2,. 3, and 4` are` changed in different,

planes, and by which the axis of directivity of the aray is shifted cyclically through four positions, two in the vertical plane, or in elevation, and two in the horizontal plane, or in train. The received impulses, when the `directive axis is` in the vertical plane, are supplied to vertical deection plates of` the Elevation indicator and produce two deections 54 and 55` thereon, each in position `corresponding respectively to one position of thedirective` axis in thel verticalplaue; That is the deection, 54 is` produced` by` the echo when the directive axis `is in oneposition inthe vertical plane and the deiiection 55 is produced by the echo when the directive axis is in the other position in the vertical plane. The height,or.extent, `Ot' these deflections is dependent upon the intensity of the received echo pulses wthich produces them. Thus, the urelation between the heights of these detlections constitutes an indication of `the direction to the remote object in the verticalplane.

i The ,t'lfrain indicator` `operates in exactly the same `way but withgespect to thehorizontal plane, and `thus `proscreen of the cathode ray oscillograph 12 than `that C `obtainable from the screen itself. To this end a` second cathode `ray oscillograph 23 is provided. The cathode ray of this oscillograph is normally'extinguished, or, cut off, as by reason of` voltage applied to the controlelectrode 24 thereof and is caused to` appear and to bedei iiected across the entire width of the screen thereof as l indicated at 2S during a very short portion of the `time duces an indication of thedirection of the remote object in the horizontal plane.` l l f l As previously stated, the Elevation, Train and Range indicators alloperate to producetheir respective indications in response to echoes received during the same brief aperture `of time, this aperture oftirnebeing but a minute fraction `of the time during which. thelcontrol operators indicator ,responds to echoes. It isdesirable, therefore, that this -aperture of time` be indicated upon the viewing `screenlof thecontroloperators indicator. This is brought -abouthycontrolling all of `theseindicators by asingle square wave pulse, indicated at E in Figs. 1, 2 and 3, and which` isproperly` synchronized in variable time relation with the radiated pulses. This pulse E I., shall refer to as the aperture pulse. This pulse is,supp1icdthrough channels later to be described, tothe control electrodes of each of the elevation, tr-ain,` andrange indicators to turn the beamen during1the Vaperture pulse,` thisbeam being extinguished` at all other times. It is also supplied to the vertical deectiongplates of the control operators indicator and produces` the square4 shouldered` deflections 36 `and 36- .as-shown in Fig. 2l and' at' the top -ofwhich v charges during the interval between these pulses. va saw-tooth wave is generated upon the condenser',

y the deflections 16 andl respectively appear, either of the latter Ytwo being produced by the echo to be selected. Thus theoperator, observlng the deflection 16, or 16', effects suitablev adjustment of the equipment to move' the square shouldered deflection 36 or 36', along the screen until the echo deflection 16, or 16', as the case may be, is superposed on it. The other indicators then respond only to this selected echo.

Having now generally indicated the character of the equipment to be described, I shall proceed with a more detailed description of its structure and operation.

In the lower portion of Fig. 2 of the drawing, I have represented at 56, by the legend Oscillator, a source of oscillations which may have a frequency of approximately 82 kilocycles, for example. This may be any suitable source of yoscillations of constant frequency, and preferably is an oscillator of the crystal-controlled type. This oscillator generates oscillations which control the entire equipment. v

These oscillations are supplied through a frequency divider 60, which produces square wave pulses indicated on Fig. 2 by the curve A. 'These pulses are also shown by the curve A of Fig. 3. They have a frequency of `656 cycles for example, and each pulse has a duration of 300' microseconds, corresponding approximately to the time yrequired for a radiated pulse to travel to a remote object miles away and return. The interval of this wave A between pulses is of about four times this length, tir-corresponds to approximately 10() miles. Of course any other ratio between the two intervals of this wave may be chosen, Idepending on the ratio between the two distance indications it is desired to produce on the screen of device 12.

Fllhis wave A is supplied to a transmitter synchronizing generator `61, which generates further pulses represented at B in Figs. l and 3 and which are supplied vover conductor `62 to the transmitter 9 where they synchronize the radiated pulses. These pulses B, as indicated bythe relation between the curves A and B of Fig. 3 are of much shorter duration than the pulses A and occur just at the end 'of the pulses A.

y In Fig. 3 the curves A to M are drawn to representv Vvoltage variations plotted with respect to the same time base. This is true also with respect to the curves N to T of Fig. 3 but the curves N to T are plotted with respect to a different time base, than are curves A to M. These time bases will appear as this description proceeds.

The pulses A are suppliedt further equipment 63l which is designated on the drawing as the control operators 100 miles blanking landsweep generator, since it generates pulses which control the horizontal sweep and short positive pulse of .the wave C. Thus,Y the cathode ray is on dun'ng the long portion y72 of the saw-tooth wave I, while it is being deflected across the screen, and oif during the short portion, or retrace period, 73 thereof while the wave is returning to the starting point of i-ts forward rdeliection. This long portion of the wave I, as previously indicated, is of a duration corresponding to the 100 mile range of the equipment, and begins slightly ahead of the corresponding transmitter synchronizing pulse of thewave'B indicated in Fig. l3.

The signal which is received from the receiver 11 is supplied through a mixer '75, ampliiier 76, conductor 77, and ampliiier '7.8 to the vertical deflection plates of the cathode.ray'foscillograph and vthus produces the vertical deections of the beam corresponding to the radiated and receivedV impulses. The signal which appears at the output of the receiver 11 may have the form represented by the curve G of Figs. 1 and 3 in which the transmitted pulse is Vindicated atv 15" and certain echoes thereof at 167 yand 17", these pulses, of course, producing the deilections 15, 116 and 17 indicated in'the circle V13 of the control operators indicator.

The control operators 100 mile blanking and sweepl generator 63 also supplies a pulse -C of the same form and frequency as the pulse C but of opposite polarity over conductor l85 to the 25 mile blanking and sweep generator 86 which in turn produces pulses, as indicated at D in Fig. 3, which it supplies to a low frequency phase shifter 4t).V This low frequency phase shifter 40', operates in a manner which will bemore particularly described in connection with Fig. 9` to synchonize an Aperture Generator 30. kThis generator produces the aperture pulses, designated E in Figs. 1', 2, and 3, and which I refer to herein by that name because they determine the brief aperture of time during which the Elevation, Train and Range indicators respond. They are variable in their time of occurrence, by variation'of phase shifter 40, and may occur at any time within the duration of the negative pulse D, as indicated by the dotted lines on curve E of Fig. 3. t

These aperture pulses E are supplied over conductor 80 to mixer 75 where they are mixed with the received signal. They are represented at 36"of the curve H of Figs. 1 and 3. They are thus supplied to thevertical Ideflection plates ofthe control-operators indicator and produce the square shouldered deflection 36er 36', indicatedV in the the cut oit periods of the cathode ray of the control operatorsl indicator 12. These latter pulses appear upon conductor `61% and are represented by theV curve C-in Figs.

2 and 3. These pulses C are of the same frequency as the pulses A and occur simultaneously therewith but are slightly shorter than the pulse A for reasons which will later be explained.

These pulses C are suppliedto the left hand contact` of the control operators range selector switch 20 and thence through thisswitch when in its left hand position, equipment 65, conductor 66, tand resistance 67 to capacity 68..The wave'C, is integrated-by the network 67, 68, i.e. potential builds up gradually across the. condenser 68 during the positive pulse and this condenser .again vdis- Thus,

as represented by thecurve I of Fig. 3.. This saw-tooth wave on condenser 68 is amplified by amplier '69 and is l t Vsupplied between the' horizontal Vdeflection plates of the the control electrode '71 of the cathode ray device 12 with rsuch polarity as to -extinguisll the cathode ray during the circles 13 and 13' respectively ofi Fig. 2. VThis deflection indicates the interval, or aperture, of Vtime during which the other indicators 23, 5t) and 51 respond and it is movable along the length of the horizontal distance 14' by variation of the low frequency phase shifter40. YIt may .thus be adjusted to embrace any time interval within that of they negative pulse D during which a desired echo, ksuch as-that indicated at 1`6is received;

lSince the echo 16 is received simultaneously with occurrence of the aperture pulse, it-appears asa further deflection at `thetop of thefdeection produced Vby the aperture pulse, the corresponding electromotive forces having been combined aidingly in the mixer 75.

Let'us assume thatthe operator, having his range selector switch 20 in the 'left hand position, observes a deiiecof the equipment and that he desires to observe this deflection Vwith greater particularity. He, therefore, rst throws the switch Z0 to its right hand position. Im-

pulses of thesame character as the impulses C but offy y opposite polarity are supplied from the control operators 100 mile blanking and sweep generator 63over conductOr 'to the control 'operators 25 mile blanking and` sweep; generator 86. This device supplies pulses of the form indicated'at D-to the right hand terminal 87'of the control operatorsVV range `selector switch.V These 'pulsesY lanode `current gridvoltage characteristic fortruev D have the time relation to` the` pulses C, lwhich is indicated by thecurves C and D of Fig. 3. It Willbe seen that l the pulses D 'are-*of the same frequency and duration as the lpulses C but that the pulses D occurl just at the end of the pulsesC and are of opposite polarity. These'pulses are lsupplied through the switch in its right handy position,l apparatus 65, and conductor 66 tothe network 67 opaques and 68 and result in a saw-tooth wave upon'the conl denser C of the form indicated at J in Fig.` A3'. This saw-toothl wave is amplified by the horizontal Vdeflection amplifier 69l .and `supplied to the horizontall deflectionl plates of the cathode ray oscillograph 12. The'wave Dl is also supplied through the 'amplifier 70 tothe control electrode of the cathode ray oscillographwith such polarity that the `beam in the cathode ray los'cillograph is interrupted during the entire .period of the long portion 72 jof.y the sawvtoothwaveand is present during the short portion 73' of the sau/tooth wave J`,this short portion 73 havingl a duration correspondingto the 25 mile interj val. Thus the ray is deflected acrossthe screen during this shortportion ofthe wave I and is blanked out during the long, "or retrace portion hereof.

The signal. and aperturepulses are Supplied to lthe` l l lvertical deflectionplates as before with thel result that the indicatonis that indicated in the circle 13 in which the deflection 16', corresponding tothe deflection 16, 1.

l l occurs more widely spaced from the deflection 15 than doesy the dellection `16l from the detlection 15. In other words, -theindicationnow produced upon the cathodel duction on lthe output current thereof. i

The operator now desires to determine with greater accuracy the distance to the object producing the deflection 16' and the direction of that object. He therefore adjusts his phase shifter l to such a position that the m.

this saw-tooth wave L has the Vsame duration as the'apen. ture pulse. i The ,saw-tooth wave on conductor 122 is` supplied through amplilier`124 to theihorizontal deflection plates of the Range indicator 23 and produces the horizontal deflection of the beam thereof across the screen. Similarly the`saW-tooth wave` on conductors 121 and 123 are supplied through horizontal amplifiers 116 and 118 respectively to the horizontal deflection plates of repro- 1 f this membergto a point on `the dial 'SS agreeingl morel n the circle 25.

the aperture pulsey is applied to it... Thus,` .the ,aperture pulse is Areproducedin itsoutput circuit and is modulated bythe received'signal, as indicated at Kin Figs. land 3. l

In these curves K the square lpulse represents the aperturepulse and the projections I `thereonrepresent the desired selected echo, all other echos having been excluded from this output'circuitr l .The wave K is appliedrthrough amplifier 34 to the control `electrode 24 of the lRange indicator. and op` crates to turn the ray on during the short portion of the saw-tooth wave on conductor 1,22. It is oil' at lall otherl times. Thus` a horizontal visible line isproduced on the viewing screen of the Rangeindicator. The intensityl of the beam, however, is varied in accordance with the rer ceived signal and is thus more intensel during the echol indicated at k. Thiaproduces .one or more bright spots .on .the screen 'of the Rangey indicator` at positions corresponding to the time in the aperture'pulse when the selected echoes are received.

l .Thus the adjustment of the low frequency phase shifter ldetermines the time of occurrence of the aperture pulse and hence the position ofl the bright spots onthe range indicator and itthus constitutes means whereby the ldistance to the remote object producing one of the bright spots may: be determined. It so happens, however, due to manufacturing variations and inaccuracies in the low lfrequency phase shifter, that the time of occurrence of the aperture pulse. does not agree, with desired accuracy, with the calibration which may be provided upon the dial, which maybe associatedwith its control member.

Suchl a calibrated ldialisindicated at 8S in Fig, 2 as col l operating With'anindex on the control memberl.l Accordingly, means are providedwhereby the adjustment of Range indicator, a large number of such pulses occurring' y for every aperture pulse and one occurring during each aperture pulse. These pulses are supplied'todhe vertical deflection plates 45 of the range indicator andiproduce the inverted V-shaped delection `indicated at 35 `in The time of .occurrence of these pulses, which I referto as target marker pulses, is varied synchronously with the variation of the aperture pulses but by reason of their high frequency their time of occurlrence may be more precisely controlled. Thus the operator adjusts his control member 89, which Varies the the Elevationiand Train indicators 50 and 51 and produce thehorizontal dellection ofthe beam thereof across the able,` preferably electron ,discharge, `circuit capable `tof transmitting the received signalto its output only when time of occurrence of both the aperture pulse and the target marker pulse until the inverted V-shaped deflection 35 coincides with the bright spot produced bythe echo. The distance may then be accurately read from the scale These target marker pulses` are indicated at `F in Figs.

2 and 3. The wave F of Fig; 3 for simplicity, indicates only that one of the target marker pulses which occurs during the aperture pulse E. Thesynchronous movement of the pulses `)E and E with respect to time is indi cated by the same pulses represented by` dottedvlines at e and f. i l p These target markerpulses F are produced `from the sine wave of lthe 82 kilocycle` oscillator 56, which sine wave is supplied to the `target marker generator 42 `through a high frequency phase shifter 44. `One of these pulses F occurs for each` cycle of the 82 kilocycle sine wave, or

for `each aperture pulse. Each pulse of wave F is muchshorter than a pulse of wave E and one pulse F occurs during a pulse E and 124 pulses of wave CF occur between each two successive pulses of Wave E.`

The two phase Shifters 40 and 44 are geared together for variation by a variable control member89 and in proper ratio to causethe` sameishift of the pulses F as of pulses .E so .that upon relatively `smallmove'rnent `of phase adjustment member 89 the aperture deflection 36 plane.

on indicator 12, and the time over which the range indicator operates shifts but slightly, and imperceptably, 'as

seen on indicator 12, still, the bright spot on indicator 25 may move considerably with yrespect to inverted V- shaped ldellection as seen on the screen of the range indicator. This indicatorV thus produces a Vernier indication foi the adjustment of the member 89 to a position corresponding to the distance to the object producing the echo. When the vertex of the inverted V equally divides the bright spot on the range indicator, the distance to the remote object may be read from the scale 08 which is arranged to cooperate with the member 89.

The control member S9 may be suitably connected or geared to a position transmission device 97, which may comprise a selsyn device whereby' the position of indicator 89 on scale 88 may be reproduced at a remote point,

as for remote control and indication purposes.

The detail structure and operation of the phase shifters 40 and 44 will later be explained in connection with Figs. 9 to 12 of the drawing.

The operator having determined the distance to the remote object producingfthe deflection yunder examination may now desire to determine the direction of this object.

array,`fsince it has a marked directional characteristic. The directional properties of thek antenna do not permit sufficiently accurate data to be obtained without the use of specially designed train and elevation indicators working together with certain special characteristics of the antenna. The operator, therefore, refers to his elevation and train indicators which are responding to the same echo and are operating only duringthe time of the same aperture pulse.

vrTo understand the operation of the elevation and train indicators it is desirable first to consider the system Whereby lvariation of the axis of directivity of the antenna system is obtained. This system comprises the antennae 1, 2, 3, and 4, the transmission lines 5, 6, 7 and 8, and the switch mechanism 52 lpreviously mentioned. This equipmentl is fully described and claimed 'in copending applications of Lawrence M. Leeds, Serial No. 410,836, led September 15, 1941, entitled Directional Radio Systern, `now U.S. Patent No. 2,412,159, and vof Richard C.

Longfellow, Serial No. 412,452, tiled September 26, 1941v entitled Directive Radio Systems now U.S. Patent No.

yOf course, a rough indication of the ydirection is obtained from the approximate position of the antenna 2,412,160, and both of which applications are assigned to the same assignee as my present application.

Each of the antennae 1, 2, 3, and 4 may comprise four .radiating half-Wave sections a, b, c, and d, the sections a and b being end to end and the sections c and ld being Aend to end and the sections aand b being spaced a half wave length from the sectionsc and d. The antennae 1 and 2 are spaced end to end and similarly the antennae 3 and 4 are spaced end to end, the antennae 1 and y2 being" spaced a half wave length .from the antennae 3 and 4 and all of the antennae being lspaced in the same The spacing of these elements inthe drawing is chosen for clarity and simplicity of illustration,

'Antennae 1 and 4 are connected together bymeans of a transmission'linel l90 through impedance matching devices '91 and 92 whereby the impedance of the unbal-v anced transmission line is matched with thebalanced impedance of the respective antennae. The antennae?. and 3 are likewiseconnected together through transmission linelr 93v and impedance matching. devices 94 and 95,

96 and thence ythrough a transmission line 98 toithe transmitter 9. A suitable point on the transmission line 98 is also connectedhthroughthe transmissionjine 10I yto the receiver 11. Of course, meansare included, which ,is represented by rectangles 10? 'to protect thereceiver from the intense pulses produced by the transmitter and to prevent attenuation of receivedV pulses by the transmitter 9.

As thus arranged, the axis of directivity of the array is varied in position in accordance with the transmission lines over which energy is transmitted between the array and the transmitter or receiver. Mechanism 52 operates to confine the transmission of energy toparticular lines thereby to control the axis of directivity of the array.

The mechanism 52 comprises a rotatable condenser hav.- ing a rotor of the shape of half of a disk, and which cooperates with a plurality ofV stator plates 100, 101, 102 and 103, the rotor being grounded as indicated at 104. Each ofthese stator plates is connected through a respective transmission line 105, 106, 107 and 108 toa point on the corresponding transmission lines 6, 5, 7, and 8. These transmission lines 105 to 108 may each have a length equal to a quarter of the wave length at the frequency at which the system operates, or an odd multiple thereof. Withthe rotor electrode in the position shown, low irnpedance is produced between ground and each of the stator electrodes 100 and y101, whereas high impedance exists between ground and the stator electrodes 102 and 103. Due to the impedance inversion effect of the transmission liries 105, 106, 107 and 108, by reason of the lengths thereof, a Ahigh `impedance is produced on transmissionrlines 5 and A6 at the points 105' and 106 to whichfthese lines are connected and similarly low impedance is produced on transmission lines 7 andS at the points 107 and 108 to which the transmission lines 107 and 108 are connected; Thus lines 7 and 8 yare disabled, being effectively short circuited at the Vpoints 107 and 108', whereas lines'rS and `6 are effective.. Points 107 and 108' are so spaced from the point 96 and also from transmission lines 90 and 93- that the short circuit at the point 107 and 108 is ineffective to disable these other lines 5, `6, 90 and 93. Thus energy is transmitted between the transmitter 9 and the array and between the array and the receiver 11 over ther lines 5, 6, 90 andv93. However, since the path over lines 90 and' 93 to the antennae 2 and y4 is longer than that to the antennae 1 and 3 the wave exciting antennae 2 and 4 isV delayed in phase with respect to the wave exciting antennae 1 and 3. This means that the beam propagated by thel antennaearray is vpropagated at an an- If the rotor of thedevice 52 now be rotated counterclockwise through 90 then transmission takes place over lines `6 and 8 with the result that the wave which excites antennae 3 and 4 is delayed with respect to that which excites antennae 1 and 2 and the axis of directivity of the system lies in the vertical plane at anangle above the fnormal ofthe array. If the rotor 52vbe rotated through thentransmission occurs over lines 7 and 8 and antennae land 3 are energized in delayed phase relation with respect to antennae 2 and 4 and the axis of directivilty Ylies in the horizontal plane latgth'e right 'of the 'normal of the array.

lf the rotor Ybe rotated through 270 the axis of directivity liesin the yvertical plane at an angle belowthe nor- Y mal of 'the array. Thus as the rotor 52 rotates the axis of directivity of the system Iboth with respect to transmission and reception rotates about the surface of'a cone through Ythe four positions in cyclical sequence.

The rotor 52' is`-driven by means of a motor 110 on the shaft to which is mounted a' generator'111, which produces a pulse such as that indicated infFigs. 1 and 3 at 112' on `the curves N.k At one pointy in each rotation Vof the condenser, rthese pulses 112 occur, their occurrence being'at a 60 cycle rate. Thesepulses-.are supplied to the square wave generator 1'13which produces a square-` waveof the :form s hown at VO in `both Figsv1 and 3.

This square wave O'is supplied o verfconductorV 115 tothe horizontaldetlection amplifier 116 of ythe elevation'indij i Y 11 t cator. `It is also supplied over conductor 117 to the horizontal deection amplifier 118 of the train indicator. jiu both cases it serves to control the steady potential about which the saw tooth outputs from these ampliiiers oscillate. These amplifiers, it will be remembered, amplify the saw-tooth wave produced by the horizontal deflection generator 120, which is controlled by the aperture pulse wave, and they operate to deect the ray of the elevation and train indicators across the screen during the aperture pulse.

These saw-tooth oscillations are reproduced at the ou-tput of the horizontal amplifiers 116 and 118 where they appear in the form indicated by the curve T on Figs. 2 and 3, the oscillation being about one axis a during one portion of the wave O and about a different axis b during the second portion of the Wave O. This is accomplished by mixing the two Waves L and O in the amplifiers `116 and118. This means that the horizontal deection of the beam of the cathode ray oscillograph occurs about one center during the one portion of the wave O and about a different center during a second portion of the wave O. Since the saw-tooth wave produced by generator 120 is of higher `frequency than thesixty cycle square wave, `the beam is deflected across `the scale a number of times about eachcenterbefore any change to the other center.

The square wave O produced by generator 113 is also supplied to a frequency doubler `140 having two output circuits 141 and 142. The frequency doubler `140 produces a square wave of the Iform indicated at P in Figs. 1 and 43 on the circuit 141, and a square wave of the form indicated at Q of Figs. 1 and 3 on the circuit 142. These waves are identical -but the wave Q is displaced in jphase by 180 with respect to the wave P. These waves P and Q are supplied to respective mixers 143 and 144V to which the aperture pulse from conductor 80 is also supplied. These mixers 143 and 144 are so arranged that no output is produced except during an aperture pulse and then only those aperture pulses which occur during the positive portion of the respective wave` P or Q. That is, the aperture pulse is reproduced at Vthe output of these mixers only during the positive portions of the waves P and` Q Theresult is that the aperture pulses appear in groups at the output of mixer 143 and 144, as indicated by the curves R and S in Figs; 1 `and` 3, which curves pertain, respectively, to the conduptors` 145 and 14,7, the groups of aperture pulses of the curve S being displaced in phase :by 180 from the similar `groups `of the curve R; The pulses represented by the curve R are supplied over circuit 145 and ampliiier 148 to the control electrode-of the train indicator, whereby they turn the beam of the train indicator on during the period of the different aperture pulses. The` aperture pulses of the wave S are supplied over circuit 147 and amplifier 146 to `the control electrode of theelevation indicator where they'turn the beam of this indicator on duringthe occurrence ofV the aperture pulses.` Y t i i y Now it will be observed from the time relationship between the curves R and O of Fig. 3 that the `beam of the Vtrain indicator is on only during the` periods ofthe aperture pulses which occur during the intervals T1 and T2 of the wave O. These are periods during which the directive axis of the array is respectively tothe right and to the left of the normal of the arraytin the vertical plane. The received signal during` these times, but onlyduring these aperture pulses, is `supplied lfrom the receiver` `11 through the mixer and clipper 31, apparatus 150, circuit 151, vertical amplifier 132 tothe vertical deflection plates of the train indicator.' Thus, when the directive of the array is to the right of normal in the Vertical plane, the beam of the train indicator is turned on during the period ofi the-aperture pulses ofthe curve R, it is swept across therscreen during the more" steep portion of `the saw-tooth wave of the curveT, which occurs during 'the aesood.

and clipper 31, which issupplied over circuit 151. It therefore produces `the deflection such as that indicated at 136 in Fig. 2 `in accordance withrthe strength of the re-` ceived signal.

When the directive axis of the array is to the left of the normal, as during the time T2, the same operation occurs but the horizontal deflection of the beam is about a different center, or the deflection starts from a dilferent starting point, as indicated by the curves O and T, and the result is, that the vertical deflection on the screen produced by an echo from thesame remote object appears, as indicated at 135, at a dilerent position on the screen.

Since the directive axis is now ditferent, the intensity of the received signal may be different, and may be smaller, with the result that the deflection 135 may be smaller as indicated, than the deflection 136, depending upon the direction to the remote object. i

-If the antenna array be rotated about a vertical axis until the heights of the two echo signals 135 and 136 on indicato-r 51 are equal, then a plane normal to that of the antenna and passing through this axis also passes through the object from which the reections are received. A selsyn position transmission system may then be employed, in a manner not shown, to transmit the position of the antenna about the horizontal axis to a central point, as was previously described with respect to range information.

The operation of the elevation indicator is exactly the same asthat of the train indicator but it occurs `during the times E1 and E2 of the wave O when the directive axis is in the vertical plane `at positions respectively above and below the normal of the array. The signal is supplied to `this device from the mixer and clipper 31 through apparatus 130, conductor 131 and amplifier 152 to the vertical deflection plates of the indicatori.`

If the antenna be rotated about a horizontal axis until the heights of the two echo pulses 54 and 55 on indicator 50 are equal, then aplane normal toithat of the antenna array and passing through `this axis `also passes through the object from which the reections are received. This locates the object in elevation and the position of the antenna about a vertical axis may be transmitted by suitable mechanism not shown, to a desired remote point.

It will thus be seen that the elevation, train and range indicators all respond onlyduring the short aperture of time which is indicated vby the deection36 or 36 upon the control operators indicator. The range indicatori-e sponds during all aperture pulses, whereas, the train and elevation indicators respond during alternate `intervals as determined by the 4groups ofaperture pulses of curves R and S. Theoperator," by means of his mechanical dcvice 89 and `the two phase Shifters, may shift this aperture of time to sucha point as to bring about the operation of the elevation, train and range indicators during ,reception o fa particular echo, whichhe may observe on the control operatorfs'indicator, and which he `adjusts the equipment to select. Hemay thus determine with the aid of the range indicator and device 89 the accurate distance to the object producing the echt, and from the elevation and train indicators the direction, oftheobject producing the echo.

As previously stated, `the aperture pulse is supplied through the mixer and ,clipper 31 and butter amplier 32 and amplifier 34 to the grid24wof the range` indicator, and it is also `supplied fromthe mixer and clipper through apparatus 130 and 150, respectively, to the vertical deflection electrodes of the elevationwand train indicators. The form of the wave produced upon'tthe conductors 33. 151 and 131'at theoutput respectively of the buiier arnpliiier 32, apparatus 150 and apparatus 130 is indicated respectively by the curves K and M of Fig. 3, the curve K applying tothe circuit 33 andthe curve M applying to .aperturepue and which is `supplied over the circuit 123; 1

` and it is deflected vertically by the signal from the mixer ,the circuits `15.1 and` 131.11".Y

The apparatus 31, and which these curves coupling condenser 166 to the control electrode of the discharge device 160. The aperture pulse, after being reversed in polarity by the polarity reverser y8-1 of Fig. l, which may be a single stage amplifier, is supplied over conductor 82 to the control electrode of the device 161.

The anode of the device 161 is coupled through a condenser 170 to the screen electrode 171 of device 160. Positivepotential is supplied to this screen electrode 171 through a resistance 172 from a tap on the bleeder resistance 173. y

Normally the discharge device 160 is biased beyond cutoi to such an extent that no anode current iiows therein, and the signal applied through condenser 166 is not normally reproduced in the anode circuit. The vdischarge device 161, however, normally passes a large anode current. The aperture pulses are supplied in negative sense to the control grid 181 of the discharge device 161 and therefore produce a reduction of current in resistance 163 during the period of the aperture pulses. The potential on the anode of this device 161 therefore rises. This rise in potential produces a rise in potential on screen grid 171 of the device 160 by reason of condenser 170. This rise in potential on screen grid 171 during the periods of y the aperture pulses produces a iiow of current in the anode of device 160 during these pulses, and of course, at this time this current is modulated by the received signal applied through condenser 166 to the control grid of the device 160. Therefore, a potential wave, such as that indicated at K, isrproduced on conductor 180, this wave comprising the aperture pulses in a negative sense, the crest of each pulse being modulated bythe received signal as indicated at k. v

This wave K may be supplied over conductor 180Yto the buffer amplifier 32 of Fig. l, amplified thereby, and supplied through the further amplifier 34 ofFig. 2 to the control electrode of the Range. indicator, thereby to produce the bright spot on the yviewing screen at the position corresponding to the received echo.

The amplifier 162 of Fig. 4 produces the wave M of Figs. l and 3. It has its cathode connected through a bias resistor 182 to ground and thence through grid resistor 183 to the control electrode thereof. This control electrode is connected through condenser 184 andresistance 164 to a variable tap 185 on resistance 163. The position of the'tap 185 and the value of resistors 164 and -165 areso chosen that the grid of device 162 is driveninthe positive direction during they aperture pulse so that the anode potential on the device 162 drops during the rperiod ofthe aperture pulse. Thus the voltlage on this anode is as indicated by the curve M in Figs. V1, 3 and 4. Y. v

Y It will be observed that the variationin current in resistance 163 produced by device 161 `during the aper- .ture'pulse tends to drivel the point 186, tov which the control electrode of device`162 is coupled, more positive, while the variation in current in resistance 165 and 164 and the lower portion of 163 produced by the aperture pulse upon discharge device '160, tends to drive the point 186. less positive.

potential in eitherdirectionas desired, during the aperfturepulse.' For reasons'prese'ntly, to be explained,l I

-14 ducing an increase-in current inthe device 160 thereby lowering the .potential atfthe point 186 in accordance with the signal during the aperture pulse. The potential on the `anode of device 16.2 during the aperture pulse then varies as indicated at k in Figs. 3 and 4.

This potential is supplied over the long conductor 151 which may be the center conductor of a concentric transmission line to the line-terminating resistance 190 which may be located near indicator 51. This resistance may be shuntedpby a potentiometer 191 the variable tap of which is connected to the grid of a discharge device 192. The anode ofl this discharge devicevis connected to ground through a path comprising condenser 193 and resistances 194 and 195, the point between resistances 194 and 195 being connected to the grid of discharge device 196. The `anodes of these two discharge devices i192 and 196 are connected together through resistances Yso l K Thus the position of the tap 185 upon resistancel v163 and the values of resistances164 and...y

` 165 maybe fso chosen Ythat the point 186 is varied in 197 and 198, the point between these resistances being connected to ground through the source of anode potential 199. The positive terminal of Ithis source is also connected through resistance 24N) to the screen grids of the two discharge devices. Proper bias for operation of the two discharge devices 192 and 196 is obtained from the cathode bias resistor 2611.

It will `be seen that the electromotive forces, which appear on conductor 151, are amplified by device 192 -and supplied in inverse phase to ltheg'rid of dev-ice 196. Thus the anode circuits of the two devices 192 and 196 operate in balanced relation to produce a voltage as indicated at M' on the anode of device 192 and as indicated at Ml on the anode of device .196.' These voltages are supplied by means of conductors 203 between the vertical detiectio-n plates of the train indicator.

Fig. 5 represents certain curves somewhat more clearly portraying the operation of the apparatus of Fig. 4. 1n this figure the signal supplied through condenser 166 is indicated by the wave 205. The aperture pulse, as supplied to the grid ofthe tube 161, is indicated by the wave 206. The aperture pulse, as it appears on the anode of discharge device 161, is indicated at 267. The signal plus the aperture pulse as it appears upon the anode of a device is indicated at 208 whereas the voltage which appears on thegrid of device 162 is indicated at 209. The voltage on the anode vof device,

162 is indicated at M. This latter voltage is supplied over the long conductor 151 to the amplifiers 192 and `196 thel anodes of which operate in balanced relation.

By4 reason of the form of the wave'M the efficiency of operation of the devices 192 and 196 is materially improved; that is, the voltage of lthewave M varies about equally Vin each direction `from the steady state y This means that the discharge devices 192 andV value. n 196 may be ybiased aty a point about midwayof their anode current grid voltage characteristics andthe full range of this characteristic between saturation and cutoff may be utilized in amplifying the wave' M. Y. f

The discharge devices 192 and 196 andthe circuits therefor, may correspond to the equiprnen'tllV ofFig., 2. A'second pair of such discharge devices, similarly connected, may be employed tocorrespond with equip-v ment 152 of Fig. 2. Of course, apparatus 130 of Fig. l includes circuits similar to those explainedl in connection Vwith, device 162 of Fig. 4 for supplying the desired voltage Wave M to the equipment 152 of'Fig'.vr 2.

The discharge devices V-160fand 161 of Fig. 4 are 1in. eluded intheequiprnent represented` by the rect-angle31 f The equipment fof Fig. Ltpossesseys'rthe advantage that the'echofis reproduced at the .output circuit asa variation from a voltage Vwhich isfunaffected byvariationfin yother signals or noise which-maybe receivedby the receiver, at times'lother'thanfdu'ring the aperture periods. ,Y This isby'ea'sonoffthe action of condenser.V

fui'-` v 166 andA` grid resistance 1.66 Vand by reasonlofthe' ther"factlthat the pulsesllS" correspondingtoth tude since they are limited in the receiver and the topsY of these pulses correspond to substantially zero `voltage on the grid of device 160. This is because the grid isprevented from going more than minutely positive by kgrid f rectification. The alternating current axis of wave `350 is indicated at 352, this being a line which divides the areas between it and the wave 350 equally. vThus the disf tance x between this line 352 yand the zero grid potential line 353 is the bias between the gridand cathode. The peak-to-peak amplitude of the pulses being constant and determined by the receiver, is of suchvalue that the l grid is alwaysat a voltage positive with respect to the value `354 which produces plate kcurrent cut off, in the de vice 160 when the screen grid is positive during the ,aperture pulse.

receiver, never approaches the cut-off valve 354 by less than the quantity, Z. 1 t

In Fig. 11b the curve 350i corresponds to curver 350 of Fig. 11a, but is drawn to represent the situation when many large echoes are received iat times other than when y the relatively smallrlesired` 'echo' 351 is received, 'the echo 351 being of the same intensity in both cases.

The alternating current axis 352 is now nearer the zero grid voltage axis 353, the quantity X non/'being smaller than before. Since, however, the quantity y is the sameas before, the quantity z is likewise the same as before. Therefore the plate current variation produced yby. echo 351 is This` wave. 219 is now impressed upon the gridv of discharge device `223 the anode of which `is also connected in parallel with ay discharge `device 224 to the grid of which the aperture pulse is also applied in knc-:gative sense through condenser 225.. The device 223 is so biased that `it-becomes conducting only duringthe period `off the aperture pulse, that is, during the portion of-the`wave`219 f above the dotted line227. Thus, the anode potential of this' device drops in .accordanceV with that portion of the wave 219 above line 227. However, because of the action of device 224 this anode potential tends torise during the aperture` pulse, the yresultant etect is that indicated at 23).

This may be better seen from Fig.f7 in whichy the'wave 231 represents the signal applied to the grid of the device v218; thecurve 232represents the .aperture pulse applied to the grids of devices 226 and 2.24; and the wave 233 represents the voltage 'whichappears on thelanodes of devices 218 and 220. The portion of this wave 233 above the dotted line 227 produces anode currentin device 223 f The most negative part of wave 350, corre`-, 'i sponding to zero received carrier wave atv the input tothe and thus tends to produce a voltage of the form indicated yat 234. This voltage, however, when combined with the aperture pulsewhich appears atkthe anode of device 224-r in the form indicatedl at 235, resultsin a wave of the form indicated at2li6y in ywhich the` voltage variation may be equal at either side ofthe steady state value.

Fig. 8 shows the equipment represented at 65 in 2.

f This gure'includes switch 20, of Fig. 2, which, when in f'switches242, 241 and 2i) are allconnected together mei about the same value of plate current asbefore being totally unaffected by the changed averagevaiue of the wave 350 hom that of wave 350.

In other words, the etTect of the kpulses. 15 peakato-peak amplitude is to tie the base of the echo 351 to a fixed position on the static characteristics of discharge device 160. Since rectitication occurs at the positive `peak of pulses 15 the negative peaks occur at a xed point on the anode current grid voltage characteristic and the echo 351 isa variation from that fixed value. This value thus remains unchanged irrespective of what happens between echo 351 'and the pulses 15". L, t 1. t.

The circuit of Fig. 4 is disclosed and claimed in a copending application of F. M. Deerhake, Serial No. 445,-

' 309, filed June 1, 1942, entitled Pulse Systems, now U.S.

Patent No. 2,416,088, and which is assigned to the same assignee as mypresent invention. p,

`In Figs. 3, 4 and 5 I have represented the aperture pulses of the wave M as modulated by |a single echo. Of course more than one echo may be received during the aperture pulse.` t i Fig. 6 represents a further 'circuit which may be employed to accomplishthe purpose of Fig. 4. In this circuit the signal is applied through condenser 215 to the grid of electron discharge, device 216 in the positive sense. This of constant deviceis normally biased toV be conducting `and its anode potential thus reduces in response` to thesignal. Thus,

the signal is reproduced uponthe anode of thisdevicein is upper position; makes contact with `conductor 64to which the wave Cis applied, and when in its lower position engages Contact 8'!` to which the wave D is applied.

This switchZ is connected to the grid of an electron disV charge device 246, which includes in yits anode circuit the twoswitches 21,k shown` within rectangle 65 of Fig. 2.

This switch includes two. movable contacts 241 and y242 each having two cooperatingstationary contacts. These "chanically by a member represented by the dotted line 243 to be moved simuitaneouslyto their upper positions and to their lower positions. If we assume that the switches kare in their upperpositionso that they waveCis applied kto the grid `ofthe discharge device, kthe anode circuit'of` the discharge device then extends as follows: From the positive terminal of the source of operating potential 244 through resistance 245 anode and cathode of discharge device 240, switch 241 in its upper position, load resistance 246, back to ground andthe negative terminal of the source of operating potential. This device 240` is normally so biased thatV little or no current flows in its anode circuit except during the positive pulses of the Wave C. This current flowing through the load resistance 246 reproduces the wave C upon this load resistance, the wave thus being supplied to the network 67, 68 of Fig; 2. This is the operation required to produce the 100 mile indicar tion of `device 12, which is indicated within thecircle 13 of Fig. 2; p

Aif switches241 and `242 Abein the lower position, then the anode circuit of the discharge device extends from the positive terminal of the source 244 through resistance 245, anode and cathode .of device 240 and switch 242 in its lower position and resistance 247, back to ground and to thenegative terminal of the source.` Wave -D is now applied to the 'grid'of the` discharge device and produces current pulses in theresistance 245 in accordance with the wave -D These current pulses result in a drop in voltage'` with respect-.to groundat the anode of `the discharge device. This drop` in yvoltage is` supplied through condenser 248 and switch`241` in itslower position,`.`to

indicatedat 219. The anode ofthis device, however, is connected in `parallel witha second discharge device 220 tothe. gridtof which the aperture pulse Ais )applied-in `negative sense; Thus the aperture pulse isv also reproduced in thewave 219 upon the anode oithese devices and appears as indicated, at 221 in'the wai/e219, `the `signal which occurs during the aperture pulse producesjthe `modulation 222 at the topof the aperture pulse 221. A

. resistance 246 where it is reproduced in` a `negative sense with` respect to thefwave fapplielptof the "grid of` the device 245'); i Inf other words, device `240` `"reverses thegfpolarity, of the `vvave .-fD -toproduce on resistance 2426the Wave .-t-'D. This is the .condition necessary:` to produce". the,` 25 lmile indication of device12-a`s indicated within circle 13' of` Fig.. t te Fig. 9 represents the high "frequency `and 1frequency rises.

l? phase Shiftersv 40 'andif'l of Fig. 2, the high frequency phase shifter being indicated in the upper portion of the figure and the low frequency phase shifter being indicated in they lower portion of the figure.y The mechanical connection between the two is indicated at 89.

Referring first to the high frequency phase shifter, the sine wave of voltage from the 82 kilocycle oscillator 56 is supplied. to two buffer amplifiers 250 and 251. This waveis supplied to the amplifier 250 directly but it is supplied to the amplifier 251 through a phase shift network 252 whereby it' is shifted in phase by ninety degrees. The outputs from these amplifiers 250 and 251, which are in quadrature phase relation, are supplied to respective coils 253 and 254,-which may be the stator coils of a goniometer, for example. a The coils l253 and 254 lare lpositioned at right angleswith respect vto each other and thus produce a rotating field` at 82 kilocycles within them. The coil 255 is mounted for manual rotation within coils 253 and 254 to have voltage induced therein of any desired time phase relation according to the position to which it is adjusted.

This coil is provided with slip rings 256 and brushes which are included in a circuit V257 whichy connects the phase shifter to the input of an amplifier and limiter 258. This amplifier and limiter 258 may be of any suitable type to produce square wave pulses at its output circuit. If we refer to Fig.V lO-e in which the sine wave applied to the amplifier and limiter is represented at 259, the square wave output may be that represented in Fig. -a at 260. This square wave voltage is supplied to the grid of an amplifier 261, the anode Vcircuity of which includes an inductance'262, a resistance 263'and4 a source of anode potential represented by the' symbol B+, the negative terminal of this source being grounded at 26.4; The square wave applied to this grid produces square wave pulses of current through the load impedance comprising inductance 262, resistance 253,'y condenser 272, resistance 273', and stray capacity 266, these pulses of current being represented by the square wave 265 in Fig. 12. "TheV stray capacity 266 exists inherently in shunt with the path comprising inductance 262, resistance 26:3, and by-pass condenser 271 and is indicated by the dotted lines 266. The

- l result is that-each change Vin current in inductance 252 is followed by an oscillatory transientr in the circuit 262, 253, 271, 256. This, oscillatory transient has a frequency determined byfthe constants of this circuit and it is much higher than the 82 kilocycle squarelwave. y This transient is indicated at 27@ in AFig. 12 where itsy first cyclev275is indicated as'of high amplitude and its later cycles being ofrapidly diminishing amplitude throughout the period of each square wave pulse.v

f This square wave 265 and its oscillatory transient 270 are supplied to the path comprising condenser v272 and resistance 273. This-path may include a source of negative bias potential 273 vfor the discharge device 280 land may terminate in ground. By reason of ,the operation of this condenser 272, the voltage of the square wave 265 is not reproduced as a square wave on the resistance 273 but rather appears thereon in the form .of the wave `rep.` resented by the dotted 1ines.274 in Fig. 13. That is, when the currentis minimuml in device 26,1 its anode is at high positive potential and the condenser 272 assumes a certain charge. During a positive pulse on thegrd of this device 2M., lcurrent increases in the anode causing condenserr 272 to discharge to a certain extent through vresistance 273. This current `produces a voltage on resistance 273 represented by the portion b of the curve 274 of Fig. 13. During the negative portion of the square wave, the current drops in device 261 and its anode potential Condenser 272r then. commences to charge and current flows in resistance 273 in accordance with the'portion a ofthe wave 274 of Fig. 1'.3, and thus the cycle repeats. It will be seen rthat the portions ,a and Ab (of the Wave 274'arel very'steep and that thetransient'oscillation previously mentioned is superposed upon this'steepwigaye: However, because of the steepness of the portion aof the wave 274, the first positive swing 275 Yof the transient cycle extends to a much higher voltage than doesthe second positive swing 276, the difference in the peakj values of these two positive swings being substantially greater than is the case in Fig. 12. i This voltage is then supplied to the grid of theV device 280 which isy vbiasedto be nonk conducting for any'voltages applied tothe grid of'value less than the positive value represented atc in Fig.v 13., Thus, in the anode circuit of theV device 280, only pulses of current suchV as thoseindicated at 275 appear. These` pulses are represented in Fig. 10-f as occurring just after the zero points ofthe 82 ldlocycle wave 259 represented in Fig. 10T-e. These pulses 275 are the target marker pulses F of Figs. 2 and 3 and ofcourse, they are shined in their time phas'erelation with respect to waves from the oscillator 56 by variation of the position ofthe rotor coil i 255 within the coils 253 and V254;V

The low frequency phase shifter and aperture generator are shown in the lowerportion of Fig. 9 'and comprise electron discharge devices 279, 281, 282, 283 .and 284. The discharge device V27.9 is supplied with operating pof tenti'al from a source 285 which is shunted by a bleeder resistance 289, la variable tap `on whichis connected to the anode through an inductance coil 290. The cathode fof the discharge device is connectedt'o the'negativeV terminal of the source2r85through a bias resistor 219,1. ,Screen grid potential s supplied to the screen grid v0f the discharge device from the positive terminal of the source 285`through a resistor 292, this screen grid'beingconnected to ground through the usual condenser 29 The wave D is applied between. the grid and the cathode of the discharge device 279`and drives the grid there of negative during the negative p ulses ofthe wave.

negative pulse ofthe wave D is, shown inFig,v 10aa. It

will be remembered that the duration thereof corresponds. to a time interval required for the wave to travel'to-an object 25 miles away and return. These negative pulses interrupt the anode current of the device 279 and thus y resistance 302 shunted by condenser 2,87, diode 281, and f a resistance 303 the latter of which is connected to a tap 320 ona potentiometer 304across the source of operatiiigy potential 285. Thusthe cathode of the diode281 is. biased positively with respect to groundrto a value greater than the positive potentialV at-3 01 by a variable amount indicated at 305 in Fig. 1 0-b,.fofr example the amount of this bias may be varied by varying the-movable.ContactY 911' Potentigmetsr 304, Thus during the rSt Portionnf the `riseY Ain voltage at point 301 corresponding to the.l dotted portion of thecurve 300, no current flows` in .the diode. Ifa voltage corresponding tothe ,horizontal line 306 of Fig. 10-,b be exceeded, however, current flows the diode and through resistance 303 to the potentiometer: 304 and thus Ytherpotential vof the cathodewof thel diode 281 becomes more positive in accordance vwith `the portion of the curve 300 above line rk306. ,increase `in positive potential of the `cathode continues ,untilthe termnation 0f the negative D `pulsewhen discharge device 27 9 again becomes conducting. The condenser ,29.4 then discharges inaccordance with theright hand portion. of the Lcurve 300 of Fig. 1,0-b. Thus the potential `on the cathodeof discharge deyice 281 is constant except during the Vlatter portion of the charging period of condenser 294.39m@ it increases and decreases in .accordance with that pgrtionof. .thecurye 13.00 which is abra/rthel12riav `"The cathodeV of diode 281 is connected through a small condenser 310, which may be 100 micro-microfarads, for example, tothe'control` electrode 286 of discharge` device 282 and through resistance 311 to ground. So long as the potential on the cathode ofthe diode 281 is constant no current flows through the condenser310 but during `the rising period `of the voltage on the cathode of diode 281, current flowsthrough `condenser 310 and resistance 311 as indicated by the portion 312 of thecurve 313 of Fig. -c. Thispositive voltage on the control electrode of discharge device 282 increases the anode current therein causing a negative voltage to be applied to the control grid` of discharge device 284 through condenser 288. This in turn decreases the anode current in the device 284 and the plate potential of that device rises driving the control electrode of device 283 in the positive direction. This causes device 283 to become conductive. This device is normally non-conducting because of the ow of anode current of device 284 through the resistance 315 which is included in the anode and grid circuit of device 283.

Anode potential on device 283 then drops forcing the control electrode of device 284 still further negative, additionally decreasing the anode current in that device. This action is `cumulative and causes an extremely rapid rise in anode potential of device 284. This is the beginning of the aperture pulse'. j

During the period of the aperture pulse, condenser 288 discharges through resistance 316 until device 284 again becomes conducting by reason of reduced negative potential onits control electrode. Anode current in device 284 causes a drop in potential on the anode of device 284 whichdrives the control electrode of device 283, which ,is` now` conducting, inl the' negative direction, reducing its anode current. Reduction in the anode current of device 283 drives the controlelectrode of device quent pulse such as that indicated at 312 of Fig. `lO--c is applied tothe grid `of device 282.` These pulses'are supplied throughcondenser 317 and a buifer and limiter 318 to the'aperture pulse bus80 of` Figs. l, 7 and 9. i,

`This aperture pulse is indicated in Fig.- lO-d and is `of a duration determined by condenser 288 and resistance 3x16.` "Preferablyit has `a duration vcorresponding approximately` tothetime required for a wave to travel from the equipment to a reiiecting surface one half mile awayand return, `or`6 microseconds, or approximatelyone cycle of the 82"l ilocycle wave., t.. A f Y 'This aperture occurs just Aat the beginning of the flow of current in diode 281, which is controlled in time fby` the adjustment of thevariable contact onrpotentiometer 304. Thus, by adjustment of the potentiometer the aperture pulse, of constant duration,` may be madeto occur at anyY desired time during the twenty-five mile interval ofpulseD.` j i `The variable contact 320 t of. potentiometer 304 is mounted on a shaft which is geared to the shaft of the rotating coil255 of the high frequency phase shifter for movement simultaneously therewith, so as to vary the time of occurrence of the aperture pulse in the twentyve mile interval of the pulse D.` t a The 82 kilocycle wave has a frequency so chosen that one cycle is of a duration required for a wave to travel approximately one mile and back. Therefore, rotation of thecoil 255 through 25 revolutions varies the phase of thewave 259 through the interval corresponding to the distance of 25 miles. The rotation of the gearing 321` between rotating contact 320 and rotating coil 25,5 is such that the contact 320 moves through its range of `movement while the coil 255 rotates through twenty-five revolu- 20 tions. In this waythe aperture pulse E of Fig. 10d and the wave 4259 of Fig. 10-e move simultaneously and synchronously and thepulse F of Fig. 10;f remains in fixed positionvvith` respect to the pulse E. Therefore, the` inverted V-shaped deection 35 seen on the range indicator remains in substantially xed position thereon. Rotation ofthe shaft 89 varies the time of occurrence in the `pulse D of both the aperture and the target marker pulse which produce the indication on the range indicator. The bright spot produced thereon bythe` received echo,` as previously described, therefore, moves across the screen of the range indicator as shaft `89 is rotated and may be made to be equally divided by the yertex of the inverted V, thereby Ato provide anaccurate .measure of the `distance to` the reflector surface by which 1t 1s produced.` This distance may be read from the scale 88` of Figs. 2 and 9. i i

As previously` explained with reference to curves A, B,

C and D of Fig. 3, the transmitted pulse, of curve B,`

occurs just after termination of pulse A. Pulse C terminates before termination of pulse A and hence before the transmitted pulses. Similarly pulse D begins before the transmitted pulses. These pulses C `and D determine the periods of occurrence of the sweep periods of the control operators indicator and therefore the transmitted pulse is indicated `on the screen of that indicator at all times as is also the aperture pulse. By rotation of shaft 89 the aperture deflection 36, or` 36', on` Eig. 2 may be moved to a position where it includes or brackets the deflection produced by the transmitted pulses. This transmitted pu`lse,.itself, then produces the bright spot on the rangeY indicator and this bright spot may be adjusted in position with Yrespect to the vertex of the inverted V-shaped deflectionproduced by the marker pulses. The position of shaft 89 `which brings about this desired adjustment,

Whichfmay` be` empirically predetermined, `corresponds to 88 in Figs.` 2 and 9` is` intended to represent any desired a mechanism for effecting such calibration.

The adjustment of shaft 89 to ya position where the radiated pulse is indicatedj'by the bright spot on the range` t indicator bisected by theinverted V-shaped deilection produced by the target marker pulses F relates the vradiated pulses to the xed time in the cycle, or period, of the 82 kilocycle Wave atwhich the target marker pulses occur. As previously mentioned these target marker pulses occur just after the zero points of' the 82 kilocycle wave 259 represented in Fig. 10-e. Since the target marker pulses and radiated pulses are indicated at the same position on the range indicator they occur simultaneously. The position of the index on scale 88 then corresponds to zero range. Of course, this ignores the time` delay in transmission of pulses in both ways between the duplexing device 98 and theantennae. j

I f shaft 89 benow rotated to delay the phase of the 82 kilocycle wave as induced in coil 255 and hence to delay the target marker pulses, the bright spot on the range indicator moves to the left unitil the delay amounts to 90 degrees of the 82 kilocycle wave, or three microseconds, or a time corresponding to one quarter of a mile of range, when it moves off the screen to the left. The delay may be increased by further rotation of shaft89 each rotation corresponding to a delay of 12 microseconds, or one cycle, or period, or 360 degrees of the 82 kilocycle wave, which corresponds toone mile of range; and this delay may be increased, as previously mentioned, through` twenty-five revolutions of the shaft 89, the index always corresponding in position on scale88 to the range from which any echowisreceived, whichecho is indicated on the range,

indicator in position bisected by the inverted. Veshaped deection.

When the delay has been increased to an extent such that an echo is received within the aperture pulse, such echo s indicated by the bright spot coming on the viewing screen from the right and moving to the left vwith increase in the delay until it is bisected by the inverted V when the echo pulse is coincident in time with the target marker pulse and the range Ais indicated by the position of the index on the scale 88.

Thus, the mechanism relates both the radiated pulse and its echo to fixed respective positions in time on the 82 kilocycle Wave, said positions being spaced apart by a number of periods of the wave corresponding toithe number of revolutions of the phase shifter `and by a time interval indicated by the position of the index on scale 88. Thus, the distance from which the echo is received is determined from the number of periods of the 82 ki-locycle wave between the radiated pulse and its received echo.

vThe 82 ki-locycle wave is, thus, the yardstick by which the time interval between the transmitted pulse and its echo is measured. The zero point of the yardstick is placed at the transmitted pulse by adjusting the target marker pulse to coincide in time withy the transmitted pulse. This is done in the initial adjustment of the equipment. The target marker pulse is then moved along the yardstick in time through a number of periods of the 82 kilocycle wave, or anumber of rotationsof the phase shifter, corresponding to the unit space markings on the yardstick, until the target marker pulses agree in time with the desired `echoes of the transmitted pulses. The position of the index on scale 88 then agrees with thev number of periods of the 82 kilocycle wave, or the number of unit space lmarkings on the yardstick, which are traversed and indicates the ltime interval, or distance, to

be determined.

The system as thus described offers vvery great advantages with respect to the observation of moving objects which cannot be seen and with respect to following the movements thereof. One of its advantages results from the four cathode ray indicators, which, in effect; serve to divide the .functions which must be performed byi-different opera-tors to -follow such a moving remote object. The control operators indicator, for example, may be positioned within easy vision of the operator who is in charge of the entire equipment. It enables him to select the remote object to be followed, and by adjustment of the aperture pulse, by control member 89, to confine the operation of the other indicators to that remote object. Y At the same time the square-shouldered deflection Von the control operators indicator aids the control operator himself in-conining his attention to the echo indication produced by the desired remote object.

The range indicator may be positionedv within easyV yvision of a second operator whose function it is to control shaft 89, thereby tomaintain the inverted V-shaped deection in position to bisect the bright, spot on'- lthe screen. This controls the indication ofdistance tothe remote object which may be made both locally Iand at a remote point as desired.

A third and a fourth operator may then be stationed to observe the train and elevation indicators respectively; These operators may also be provided with controls whereby they position the antenna array in train and in elevation respectively to maintain the two deflections onthe respective indicators o-f'equal height. This maintains the array directed at the remote object to be observed.

Thus, the functions performed by each of these operators is relatively simple, the operation being Vsuch thatV each operator may give his undivided -attention to such finindividual relatively simple function. In thiswaythe following of the remote object may be effected-'with the in- Acreased reliability with which the individual operators perform their individual lsimple functions-as compared 22 with that which may be had if asingle operator were ref', quired to observe the different instruments and operate all of the necessary controls.

While I have shown a particular embodiment of my invention, it will, of course, be understood that I do not wish to be limited thereto, since various modifications- .both -in the circuit arrangement and .in the instrumentalities,

employed may be made, and I contemplate by the ap.d

pended claimsto cover any such modiication as falls.

within the Vtrue spirit and scope of my invention.

. What I claim as new and desire, to secure by Letters Patent of the United States, is:

l. The combination, in a radio echo apparatus, of

meansrto transmit a radio pulse and to receive echoes corresponding to the time of reception of said echo.

v 2. The combination, in a radio echo apparatus, of means to transmita radio pulse and to receive echoes4 thereof, a cathode ray device having a viewing screen, means to supply `to said cathode ray device two pulses, one shorter than the other and both shorter than the interval over which echoes are received, means to deect' the beam of said device across a predetermined path on v said screen during the longer of said pulses and to deilect it from said path during the shorter of said pulses, means responsive to a received echo during saidlonger pulse to vary the intensity of said beamlthereby to vary the intensity of illumination of said pathk at the point corresponding to the'time of reception of said echo, and means to vary the time of occurrence of said shorter pulse to produce coincidence between said point and the deflection from said predetermined path produced by the shorterl pulse.

variable in time phase synchronously with saidV short pulse, meansto produce from said electromotive force a vfurther pulse occurring during said short pulse, indicating vmeans responsive to echoes received'during said short* pulse, and means responsive to said further pulse to control. said indicating means. f

4. The combination, in a pulse receptionV system inY which periodically recurring trains of pulsesare received, each of said/trains comprising an intense pulse followed` by a succession of pulses of varying intensity, of a discharge device having an anode circuit, a cathode, and a control electrode, means to limitrsaid intense pulses toy pulses of constant amplitude at least as great as the most intense of said following pulses and to supply said trains of pulses between said grid and cathode, means 'to produce peak rectification of said intense pulses `between said grid and cathode thereby to provide` a fixed bias from which the individual pulses vof said trains vary, and means to render said discharge dew'ce conducting only duringA W the period of a selected portion'of said' pulses whereby said selected portion' of said pulsesv is reproduced ins'aiv'lvv 3. Inv an echo apparatus, means to produce -periodic i "anodecircuit `as a variation from a valuev of current in said anode circuit constant irrespective ofthe intensity,

of other pulses of said trains.

y5. Infcombination, an yelectron discharge device having an anode, a cathode, and a control'electrode, fan anode to cathode operating circuit for said device, means to supply! between said control electrode and cathode trains of pulses, each `train comprising'a; strong puise of ycon-` stant amplitude land other weaker pulses` otxvaryingamyplitude, means to produce peak recticaticn of said strong essonne pulses thereby to produce a'constant'bias voltage between y s the grid and cathode, said bias voltage being of a value less than the value which cutsk offr the current flowing from the vanode to the'cathodey offsaid tube rwherebyeach 'pulse is reproduced iu saidoperating circuitas a variation deflect said ray across said screen in eitherfof two different desired time intervals and to control said ray during ysaid lintervals in` 'accord with' the iehoes received, said means comprising `means to generate a square wave, means vto "integrate said wave, means @to deect said ray in accord with; thev rwave`r resulting from said integration,

and'means to control said square wave :tc produce 'said deflection in either-,of said two desiredfintervals.

7; The'combination, in an echo apparatus, of a cathode f ray device having a viewing screen, means to deect said rayecross said screen in either of two different desired time intervals 'corresponding to dierent ranges from wave 'supplied to' said 'rsistance to interrupt said during the retrace periods thereof.y i

T10. ,The combinationfinfan Vecho apparatus; of' means toradiate periodic pulsesr-andfto receive echoes vtheredf;j

said` means comprisingiamiiiiective antenna, meansrtofy alternate the directivepattern"oflfsaid antenna between two positions at a`predetermined;ffrequcncy, a cathode ray device havinga viewing screen, means to deiect` the ray across said screen during ay short portion fof" the period betweenisaid periodic pulses, meansto control saidrayin: accord with an echo received duringrsaid short period, and kmeans tovvaryy the' center about which said deflection occurs' in the ydirection in which said deection occursV between twoy points on said screen-in thejtracez over which saidf ray'is deflected ,synchronously with said alternation `whereby echoesreceived during `said short portionof said period produce two `.indications side by side jon said; screen alonglsaid trace over which saidA ray is deected'by said deiiection means one being pro duced by echoes received when said pattern is in` one position and ythe other ,being produced by echoes received when said pattern is in its alternate positiom ll.`The combination'in an echo apparatus, of meansA v to radiate periodicJ pulses and to receive echoesthereo,

said means comprising av ydirective antenna, Anieans tov rotatethe directive pattern of said antenna throughfour positions` in v succession two` in train, and two `in elevation,` a pair of cathode raydevices having viewingsscieens," means to Aindioateon oneof said screens pulses received when-saidfpattern is in `said positions in train, andto indicate' on ther other ofsaid screensy pulsesreceivedy when said pattern is in said positions in elevatiomsaid" f indications on said screens being in positionsthereon corresponding to the respective *position of `said pattern, and

which echoes are received, said rmeans comprising 'means f f to generate either of two square Waves in accord with their f time yintervalof deflection desired, one oftsaid waves cornprising rperiodic positive pulses andthe other periodic"H7 negative pulses, said' pulses being short relative to the yperiodbetween said `pulses and occurring substantially end to end in time, means to integrate said pulses, and

means to control said deection in accordwith the Wave produced by said integration. t v 8. The combination, in an echo apparatus, of a cathode ray device having a viewing screen, meansto deflect said ray across said screen in either4 of two different desired time intervals `corresponding to different ranges from which echoes are received, said means comprising means to generate either of two square waves in accord with the range desired,` one of said waves comprising periodic:

positive pulses and the other periodic negative` pulses, said pulses being short relative to the period of the pulses and occurring substantially end to end in time, a

resistance and a condenser, means to supply either one of said waves or the other, as desired, through said` resistance to said condenser, and means to control the deection of said ray in accord with, the potential on said condenser.

`9. The combination, in an echo apparatus, of a cathode ray device having a viewing screen, means to deect saidA ray across said screen in either of two different desired time intervals corresponding to different ranges from whichechoes are received, said means comprising means to generate` either `of `two square waves in accord with the time interval of deection desired, one of said waves comprising periodic positive pulses and the other periodic negative pulses, said pulses being short relative to the period of the pulses and occurring substantially end to end in time, a resistance and a condenser, means to supplyeither lone, of said waves `or the other, as desired, through said resistance to said condenser, means to coutrol `the defiectionof said` ray `in accord with the potential on said condenser, andnieans responsive `to said square` `said antenna through four positions `'about the surface ftensity; of vthe received 'pulses from which they are means toyvary said, indications in accord withithe intiro'` duced. t

12. The combination, in an echo apparatus, of means to radiate periodic pulses and to receive echoes thereof, said'means comprising adirectivey antenna, means tok rotate thedirective pattern of said antenna through `four positions about the surface of a cone in successive order, a pair of cathode ray devices, each having a viewing screen, means to operate said cathode ray devices alterna `tively to indicate on theirrespective screens echoes re-` ceived when said pattern is in respective pairs of saidfour` positions, said `echoes received when said pattern is in-` opposite positions of each pair being indicated in corre-n sponding positions on the respective screen, and means to vary each indication in accordance with thelintensity vof the echo received when said `pattern is in the respective position. Y t

l3y'1`he combination, in an echo apparatus, of means" to radiate periodic pulses `and to receive echoes thereof-` ovcrta predetermined interval, said means comprising a directive antenna, a pair of cathode ray direction indi# cators, each having a viewing screen, means to supply echoes received during a small portion of said interval to each offsaid indicators to produce avisible indication on the screen thereof, means to`rotate the directive axis of of a cone,rechoes received when said axis istinrone pair of opposite positions being supplied to lone of said indicators and those received when said axis is in the alternate pair of opposite `positions being supplied to the other indicator, and means to produce said indications of said` echoes on each viewing screen in two positions each corresponding to a respective one of the corresponding pair` of positions of said axis. i

14.` The combination, in pulse echo apparatus, ofg

` means to `transmit periodic radio pulses and to receiver echoes thereofjbetween the` transmitted pulses, two cath-- ode ray devices, means to Vdeect :the ray of one of said devices across its screen with a given sweep velocity dur, ingthe time interval `of reception ofj said'` echoes and toT` 25 26 produce variations on the screen at points corresponding References Cited in the le of this patent to the times when echoes are received,.means to supply UNITED STATES PATENTS to the other of said devices two periodic pulses, one p 81101161' than the other and occurring during the other 2,098,287 Gent NOV- 9, 1937 `and both being short relative to said time interval, means 5 2,118,518 NePmaml May 24, 1938 to deect the beam of said other ydevice across its screen n 2,120,971 1331163 June 21, 1938 during the longer of said two pulses with a sweep velocity 2,189,549 Hfshbelgel' Feb- 6, 1940 greater than said given velocity and ,to produce variations 2,216,707 George 00t- 1, 1940 therein recognizable on the screen at points correspond- 2,227,598 Lyman et al- 1211- 7, 1941 ing to vthe times 0f occurrence of received echoes and of 10 2,231,929 Lyman Feb- 18, 1941 occurrence of said shorter pulse, means to supply the 2,261,645 Delvaux NOV- 4, 1941 longer of said pulses to said one device to produce a 2,280,524 Hansen API'- 21, 1942 recognizable variation on the screen ,thereof at a point 2,345,932 G0111d APl'- 4, 1944 corresponding to the time of occurrence of said longer pulse, and means to vary the phase of said t-Wo pulses 15 FOREIGN PATENTS in time to produce coincidence of said two recognizable 113,233 Australia a June 2, 1941 variations on said other screen. 

